The HDMI (High Definition Multimedia Interface) standard defines a physical (cable) and logical (signaling and control protocol) interface for the transfer of high definition video and audio data between a device holding the data and a device for presenting the associated information contained in the data.
The device holding the data, or source device, may be a video or audio record/playback device. The device for presenting the associated information may be a displaying device, such as a television, or an audio amplification and speaker system, and is known as a sink device.
Typical data transfer rates are such that significant power is required by the source device in order to drive the data lines in the cable and power the circuits processing the stored data in order to transmit it down the cable.
The source device may also be portable equipment and as such will be battery-powered. The power needed for processing the data and that needed to drive the cable are such that many portable devices will only be able to function for a short time before requiring re-charging. This would mean, for example, that the user would have to be content with only watching short films or accept to plug in the charging equipment for the portable device.
Thus there is a need for improving the autonomy of battery powered source devices whilst they are transferring data over an HDMI interface.